[P]

Hi Guys. This is just a thought and I wondered what you would think. I used to use Si grease or PTFE tape on ground glass joints on my vac line. Both work well but can be fiddly (grease can contaminate if over applied and the PTFE tape can be fiddly to apply and keep a good vacuum).   I saw that someone mentioned on another forum that you could buy glass joints coated with PTFE, but they were expensive. (you can apparently get pure PTFE joints, but they can suffer from thermal expansion).

Here's the idea  -  You can now get PTFE spray cans which spray a PTFE coating onto a substrate.  Therefore - could you spray your glass stopper (at the join)  with a fairly generous coating of PTFE from a can to get the same result as these expensive PTFE coated glass joints?  I no longer work in an organic lab or have a vac line so I wont be able to try this out.  What do you think? Will this work?

[macman104]

Well...I've never had any issue with a vacuum line and ground glass joints, so I'm not sure what the point of the PTFE tape is...The joints are made to fit together to form a seal, you shouldn't need anything to enhance the vacuum seal.

[P]

It's quite common to put grease around the seal to stop them sticking together and to help achieve a better vacuum. In fact it's recommended. Without the grease you won't get the pressure as low as you might do with it.  Some people use PTFE tape for this, but I always preferred grease.  It depends on how low a pressure your after. If your vacuum distilling something with a really high b.p. then you may need that extra bit of reduced pressure to get the b.p. down to a manageable temperature.

Another reason would be to stop air seeping in through the ground joint which could scupper any really oxygen sensitive reactions.

[agrobert]

What about the Teflon sleeves that are common for reaction flask ground glass joints.

[DrCMS]

We always used Apiezon black wax on all the glass joints on our vac lines.  That and used high vac hollow taps.  I think we could go down to ~0.001mmHg with our set up.

[P]

What about the Teflon sleeves that are common for reaction flask ground glass joints.

Yea  -  they are probably quite good.  It's just that someone on another forum mentioned teflon coated glass joints and said that they were expensive. I just thought that it would be simple enough to get a glass joint and spray some teflon on - much cheaper than buying a manufactured one (if it worked).

[agrobert]

why don't you try it?